1. Field of the Invention
One aspect of the present invention relates to an automated computer-implemented method and system reorienting emission computed tomographic (ECT), for example, single photon emission computer tomography (ECT) or position emission tomography (PET) heart images. More specifically, this invention relates to a method and system for aligning and centering ECT myocardial perfusion images.
2. Background Art
Emission computed tomographic (ECT) cardiac imaging can be used for the diagnosis of patients with coronary heart diseases (CHD), for example, patients with myocardial infarction or angina pectoris. An ECT heart study can be utilized to determine whether a patient's heart muscle or myocardium is healthy, diseased or scarred. In a typical study, two ECT image sets of a patient are acquired; the first after injection of a radiotracer of heart blood flow while the patient is at rest; the second after injection while the patient is performing a treadmill exercise stress test. If a particular region of the heart demonstrates reduced blood flow in both the rest and stress image sets, then it is likely that the heart muscle in that region is secured. If a particular region of the heart displays normal blood flow at rest but reduced blood flow in the stress image, this indicates that the coronary artery providing blood to that is at least partially blocked, narrowed or stenosed. If a particular region of the heart is bright or normally perfused in both the rest and stress images, it is likely that the blood supply is normal and that particular region or the heart is healthy.
Typically, two-dimensional ECT images (tomographic slices) are generated orthogonal to (short axis slices) and parallel to (horizontal and vertical long axis slices) the heart's left ventricular (LV) long axis. FIGS. 1a-1d depict a three-dimensional rendering of the left ventricle and the typical slicing of the left ventricle into short axis and horizontal end vertical long axis sections. FIG. 1a depicts a three-dimensional rendering of the LV within a coordinate system. A short axis slice is shown in FIG. 1b, a horizontal slice is shown in FIG. 1c, and a vertical long axis slice is shown in FIG. 1d. While a short axis slice, as depicted in FIG. 1b, is generally circular, the long axis slices, as depicted in FIGS. 1c and 1d are generally horseshoe shaped. Short axis two-dimensional images can be generated at discrete positions along the LV long axis between the base and apex of the heart, as depicted in FIG. 1a. Horizontal long axis images can be generated at discrete positions along the short axis of the heart between the anterior and posterior walls of the heart. Vertical long axis images can be generated at discrete positions along the short axis of the heart between the septal and lateral heart walls.
The optimal diagnostic accuracy of ECT myocardial perfusion studies requires the proper orientation, i.e. exact alignment, of the ECT images for visual and quantitative comparisons of one study to the other. Misalignment of the walls of the left ventricle between serial studies (e.g. stress and rest), can cause false diagnoses. Misalignment is commonly caused by failure to exactly position the patient in the ECT scanner for each of the two or more studies. In large and/or acutely ill patients this can be virtually impossible to accomplish. Misalignment also commonly occurs during the processing of the studies into tomographic slices. There have been many prior art proposals for minimizing the image artifacts caused by an inaccurate registration and alignment of patient studies.
The approaches proposed thus far usually necessitate manual and interactive efforts to address misalignment. In light of the foregoing, an automated method and system for realigning and centering ECT myocardial perfusion images is needed. What is needed is a computer-implemented method or system for automatic alignment and centering of ECT cardiac images about the heart's left ventricular (LV) long-axis.